The present application claims priority on Japanese Patent Application No. 2002-45204 filed on Feb. 21, 2002, Japanese Patent Application No. 2002-46444 filed on Feb. 22, 2002, and Japanese Patent Application No. 2002-46445 filed on Feb. 22, 2002, which are herein incorporated by reference.
1. Field of the Invention
The present invention relates to a printing apparatus, a storage medium having a program recorded thereon, a correction pattern, a computer system, and a printing method.
2. Description of the Related Art
(1) In recent years, inkjet printers in which a print head, for ejecting ink, is provided on a cartridge that performs scanning in the main-scanning direction and in which printing is performed by ejecting ink while scanning with the cartridge have become popular as an output apparatus of a computer. Among such inkjet printers are those that include a function for “bidirectional printing,” in which printing is carried out by ejecting ink during the forward pass as well as during the return pass, in order to increase the printing speed.
When performing bidirectional printing, it is necessary to correct the positions where the ink droplets land during the forward pass and the return pass because the image will be deteriorated if the ink droplets land in different positions in the main-scanning direction during the forward and return passes. For this reason, the printers are configured so that a plurality of correction amounts can be set, and a user or the like selects an appropriate correction amount and sets it for the printer.
One method for selecting the correction amount is, for example: to print, during the forward pass printing, vertical lines that extend in the sub-scanning direction and that are printed with a constant spacing therebetween in the main-scanning direction using nozzles at the front of the print head; and then, taking vertical lines, which connect straight to the above-mentioned vertical lines when printed in ideal positions, as a reference, to print, during the return pass printing, a plurality of vertical lines that are shifted in the direction in which the above-mentioned correction amount increases and in the direction in which it decreases using the nozzles at the rear end of the print head. The user visually confirms that the vertical lines printed during the forward pass and the vertical lines printed during the return pass of the thus-obtained print pattern have been printed in a straight line, and then selects that correction amount.
However, because the correction amounts are extremely small, it is difficult to visually ascertain whether two vertical lines arranged next to each other front to back are lined up in a straight line or are misaligned, and there is a possibility that the user, for example, may make an incorrect selection.
(2) In recent years, a type of color printer that ejects several colors of ink from its head has gained wide popularity as an output apparatus for computers. Some such inkjet color printers have a function for performing so-called “bidirectional printing” in order to increase the printing speed.
Also, inkjet printers were only capable of reproducing each pixel according to binary values of on and off; however, in recent years, multivalue printers that are capable of reproducing a single pixel with multiple values, such as three or more values, have also been proposed. Multivalue pixels can be formed by ejecting ink droplets of the same color for a single pixel in a plurality of sizes, for example.
When performing bidirectional printing using a multivalue printer, with which a plurality of ink droplets are ejected for a single pixel, the image quality may be deteriorated due to differences in the printing characteristics in the forward pass and in the return pass. For example, when the positions where ink droplets of various sizes land in the main-scanning direction are different during the forward pass and the return pass, the image quality is deteriorated as a result.
(3) Printing apparatuses such as inkjet printers comprise: a print head that ejects ink and that is provided on a carriage which performs scanning in the main-scanning direction, and a carrying device that carries a print sheet by a constant carry amount. Such printing apparatuses print by sequentially carrying the print sheet in correspondence with the printing operation of the print head. Thus, in order to achieve good printing, it is necessary to accurately carry the print sheet, and one method for this is disclosed in Japanese Patent Application Laid-open Publication No. 11-49399 (U.S. Pat. No. 6,101,426), which discloses a printing apparatus provided with a carrying device. A carry error, which appears at a specified period as the carry roller for carrying the print sheet rotates, is measured for the carrying device, this period is divided into a plurality of sections, and correction values of the carry errors for each section are set to the carry device during the manufacturing stage; the carry device carries the print sheet after the carry amount is corrected using the correction values.
However, for example, differences in the environment in which the printing apparatus is used, differences in the amount of change in the shape of the carry roller due to the thickness of the print sheet, and differences in the coefficient of friction among different types of print sheets, may change the carrying of the print sheets. This results in the problem that even if correction values for carry errors are set during manufacturing, the correction values that are set in the manufacturing stage may not always be the most appropriate depending on the usage environment of the user or the print sheets that are used, leading to instances where the print sheet is not carried appropriately.
Thus, a configuration that allows the user to correct the carry amount is preferable; however, if, as in the above, it is desired that the print sheet is carried with enough accuracy that the slightest change in the condition of the carry roller has to be corrected, then, to perform a more accurate correction, it is necessary to increase the number of sections into which the period is divided and to allow a large number of correction values to be set to each section. However, if the number of sections or the number of correction values is increased, although it may be possible for the user to correct the carry amount, it is difficult for users to determine an appropriate value for the correction amount, and no proposal has been made for determining means that allow this to be determined easily.